Background and Purpose: We have previously reported that cerebral blood flow decreased and oxygen extraction fraction and cerebral blood volume increased in pediatric patients with moyamoya disease, whereas these values did not change significantly in adult patients. In this study, we measured the cerebrovascular response to hypercapnia using 15O H2O positron emission tomography (PET) in each group of patients. These data were also compared with the oxygen extraction fraction and transit time (cerebral blood volume/cerebral blood flow) measured by 15O PET. Methods: The subjects consisted of 20 patients with moyamoya disease (7 pediatric and 13 adult patients). Cerebral blood flow was measured by the 15O H2O bolus injection method at the resting stale and during the inhalation of 5% CO2. Cerebrovascular CO2 response was estimated as the percentage change of cerebral blood flow per 1 mm Hg change of PaCO2. Oxygen extraction fraction and transit time were measured by the 15O steady-state method. Results: Cerebrovascular response to hypercapnia severely decreased over the cerebral cortices in both pediatric and adult patients with moyamoya disease when compared with those of normal control subjects, and there was no significant difference between pediatric and adult patients. A significant correlation was observed between the CO2 response and transit time, whereas no significant correlation was seen between the CO2 response and oxygen extraction fraction. Conclusions: Our study revealed that the cerebral hemodynamic reserve capacity decreased to an equal degree in both pediatric and adult patients with moyamoya disease. This finding may thus help to explain the occurrence of transient ischemic attack in adult patients.
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